"Maybe we'll be able to block this reservoir seeding," says Dr. Deborah Persaud of the Johns Hopkins center.

Photo: Associated Press

"Maybe we'll be able to block this reservoir seeding," says Dr....

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This image released by the University of Mississippi Medical Center shows Dr. Hannah Gay, a pediatric HIV specialist at the University of Mississippi, Friday, March 1, 2013. A baby born with the AIDS virus appears to have been cured, scientists announced Sunday, March 3, 2013, describing the case of a child from Mississippi who's now 2½ and has been off medication for about a year with no signs of infection. "I just felt like this baby was at higher-than-normal risk, and deserved our best shot," said Gay. (AP Photo/ University of Mississippi Medical Center, Jay Ferchaud)

Photo: Jay Ferchaud, Associated Press

This image released by the University of Mississippi Medical Center...

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Dr. Deborah Persaud of Johns Hopkins' Children's Center treated the toddler who had HIV - and now is virus free.

"Cure" is a tricky word in the field of medical research, and especially so among HIV and AIDS scientists - it's not easily defined, and given how it can raise hopes and expectations, it's not a word thrown around thoughtlessly.

So it was stunning news this month when a team of researchers announced at an AIDS conference that a Mississippi toddler had been cured of HIV. Infected at birth, the baby had been put on a heavy-duty regimen of HIV drugs, and two years later - after the child had been taken off the medication, against doctors' orders - she was virus free.

The report on this child was thrilling, and news about her buzzed through the HIV medical community. But it wasn't long before doctors and scientists began to have doubts about her case, and what it might mean in the desperate hunt for a universal cure for HIV.

The Mississippi case adds to growing evidence that HIV drugs can prevent, and may even cure, infection in the earliest stages after exposure to the virus. But scientists say that this one case - and a handful of other anecdotal cases like it - provides only tantalizing clues for curing HIV, not a go-to treatment that would be practical or advisable for the vast majority of patients.

Window to knowledge

That said, the real value of the case might be in its contribution to scientists' understanding of how HIV spreads in the human body, and how it might be stopped.

"Every angle we get into this, all of it is giving us information to beat the virus. That's why there's such enthusiasm about this case," said Dr. Susan Buchbinder, director of the HIV research section of the San Francisco public health department. "It may not be directly applicable to everyone, but this is how we're going to get a cure. You get those first steps and insight, and then you build on them."

The state of HIV/AIDS treatment now is that most patients seem able to live with their viral infection for many years, even decades, as long as they stick to a strict, daily regimen of multiple antiretroviral drugs.

The discovery of those drugs and their ability to save the lives of HIV victims has been remarkable, and utterly changed the scope of the global AIDS epidemic. But the treatment is far from ideal.

First, it's expensive, especially when patients must remain on the drugs for the rest of their lives. And whether from the unpleasant side effects, limited access to health care or dozens of other complications, it can be difficult for many people to keep taking the drugs.

In the United States, it's thought that only a third of people with HIV infections are regularly taking antiretroviral drugs; in other parts of the world, the rates are far lower. That's why a cure remains the ultimate goal.

"It's become clear that treatment, lifelong treatment with antiretroviral therapy, will not break the backbone of this epidemic," said Dr. Mike McCune, chief of the UCSF division of experimental medicine. But "early treatment might allow for some individuals to eventually come off any treatment later, and that's very exciting."

Second of two cases

The child in Mississippi is being touted as only the second documented case in the world of a person being cured of HIV. The first case - a man known as the "Berlin Patient" who was treated in Germany and now lives in San Francisco - involved a bone marrow transplant that essentially wiped out his immune system and replaced it with one that was HIV-resistant.

That doctors were able to cure him is remarkable, but the treatment was so risky, expensive and difficult that it's an impractical solution for almost all other HIV patients.

The same might ultimately be argued for the Mississippi child.

That baby was born to a mother who hadn't received any prenatal care, and didn't even know she was HIV-positive until she showed up at a hospital, already in labor.

For pregnant women who are HIV infected, treatment with antiretroviral drugs almost always prevents transmission of the virus to the fetus. There are at most only a few dozen cases of mother-to-child transmission of HIV in the United States every year, because doctors have learned to aggressively test and treat pregnant women.

So cases like the baby in Mississippi are rare. By the time that mother was tested and diagnosed with HIV, it was too late to give her antiretroviral drugs to prevent transmission, so doctors believed the baby would likely be infected, and sure enough, tests immediately after birth showed high levels of the virus in the infant's blood.

A rare decision

That's when doctors made the highly unusual decision to put the baby on a full regimen of antiretroviral drugs within 30 hours of birth. Typically, doctors will give a much smaller dose of drugs when they suspect an infant to be at risk of being infected by his or her mother.

In the Mississippi case, the drugs did their job and the baby's viral loads fell, until the virus was no longer detectable. The child was supposed to remain on the drugs - presumably, for the rest of her life - but after a few months she and her mother fell out of the health care system and she stopped the regimen. Doctors only realized this when the mother returned two years later.

They tested the toddler, and found no trace of HIV. She appeared to be cured.

Shortly after the Mississippi case was announced, scientists in France published similar results in 14 adult patients. Those people all had recently - within a few months - become infected with HIV and were given high-dose antiretroviral drugs. The patients were able to clear the virus from their blood and, eventually, stop taking the drugs.

As with the Mississippi baby, the assumption with those adults is that they were treated early enough after becoming infected that the drugs were able to wipe out the virus before it could establish the infamous viral "reservoirs" that plague most HIV-positive people.

Reservoir focus

Doctors believe that these reservoirs of inactive virus hide in the body and avoid antiretroviral attacks, only to re-activate and spread if patients stop taking drugs. Essentially, on treatment patients are able to go into remission, but that remission can never become a cure as long as the viral reservoirs remain.

That's why the reservoirs have been the primary focus among scientists searching for a cure to HIV.

But very few adults are diagnosed with HIV soon enough after exposure to prevent the reservoirs entirely. And for infants, it would be far from ideal to give massive doses of antiretroviral drugs to every infant born to an HIV-positive mother. Antiretroviral drugs can be toxic to newborns and have unpleasant and even deadly side effects, and a massive load of drugs may not be necessary.

"It's very tempting to say let's just give this to everyone. But based on the one case, is it worth it?" said Dr. Deborah Cohan, medical director of the Bay Area Perinatal AIDS Center at San Francisco General Hospital. "We don't want to throw the whole kitchen sink at the baby. Certainly if we were to do this, it would be in very limited cases."